Light emitting devices having light coupling layers with recessed electrodes

ABSTRACT

A light emitting device comprises a first layer of an n-type semiconductor material, a second layer of a p-type semiconductor material, and an active layer between the first layer and the second layer. A light coupling structure is disposed adjacent to one of the first layer and the second layer. In some cases, the light coupling structure is disposed adjacent to the first layer. An orifice formed in the light coupling structure extends to the first layer. An electrode formed in the orifice is in electrical communication with the first layer.

BACKGROUND

Lighting applications typically use incandescent or gas-filled bulbs.Such bulbs typically do not have long operating lifetimes and thusrequire frequent replacement. Gas-filled tubes, such as fluorescent orneon tubes, may have longer lifetimes, but operate using high voltagesand are relatively expensive. Further, both bulbs and gas-filled tubesconsume substantial amounts of energy.

A light emitting diode (LED) is a device that emits light upon therecombination of electrons and holes. An LED typically includes a chipof semiconducting material doped with impurities to create a p-njunction. Current flows from the p-side, or anode, to the n-side, orcathode. Charge-carriers—electrons and holes—flow into the p-n junctionfrom electrodes with different voltages. When electrons meet holes, theelectrons recombine with the holes in a process that may result in theradiative emission of energy in the form of photons (hν). The photons,or light, are transmitted out of the LED and employed for use in variousapplications, such as, for example, lighting applications andelectronics applications.

LED's, in contrast to incandescent or gas-filled bulbs, are relativelyinexpensive, operate at low voltages, and have long operating lifetimes.Additionally, LED's consume relatively little power and are compact.These attributes make LEDs particularly desirable and well suited formany applications.

Despite the advantages of LED's, there are limitations associated withsuch devices. Such limitations include materials limitations, which maylimit the efficiency of LED's; structural limitations, which may limittransmission of light generated by an LED out of the device; andmanufacturing limitations, which may lead to high processing costs.Accordingly, there is a need for improved LED's and methods formanufacturing LED's.

SUMMARY

In an aspect of the invention, light emitting devices, including lightemitting diodes (LED's), are provided. In an embodiment, a lightemitting device includes a substrate, a p-type Group III-V semiconductorlayer adjacent to the substrate, an active layer adjacent to the p-typesemiconductor layer, and an n-type Group III-V semiconductor layeradjacent to the active layer. A light coupling structure adjacent to then-type Group III-V semiconductor layer includes one or more Group III-Vsemiconductor materials. The light coupling structure includes anorifice extending to the n-type Group III-V semiconductor layer. Anelectrode formed in the orifice is in electrical communication with then-type Group III-V semiconductor layer.

In another embodiment, a light emitting diode includes a substrate and afirst layer adjacent to the substrate, the first layer having one of ap-type Group III-V semiconductor and an n-type Group III-Vsemiconductor. A second layer adjacent to the first layer includes anactive material configured to generate light upon the recombination ofelectrons and holes in the active material. A third layer adjacent tothe second layer includes the other of the p-type Group III-Vsemiconductor and the n-type Group III-V semiconductor. A light couplingstructure adjacent to the third layer includes one or more Group III-Vsemiconductor materials. The light coupling structure includes anopening extending to the third layer. An electrode disposed in theopening is in electrical communication (e.g., ohmic contact) with thethird layer.

In another embodiment, a light emitting device includes a first layer ofa first type of Group III-V semiconductor material and a second layeradjacent to the first layer. The second layer includes an activematerial configured to generate light upon the recombination ofelectrons and holes. A third layer adjacent to the second layer includesa second type of Group III-V semiconductor material. A light couplingstructure adjacent to the third layer includes a third type of GroupIII-V semiconductor material. The light coupling structure includes anopening extending through at least a portion of the light couplingstructure. An electrode adjacent to the light coupling structure is inelectrical communication with one of the first layer and the secondlayer. In some cases, the third type of Group III-V semiconductormaterial is different from the first type of Group III-V semiconductormaterial and the second type of Group III-V semiconductor material.

In another aspect of the invention, methods for forming light emittingdevices, including light emitting diodes, are provided. In anembodiment, a method for forming a light emitting device includesproviding, in a reaction chamber (or a reaction space if the reactionchamber includes multiple reaction spaces), a light coupling structureover a substrate. The light coupling structure includes an openingexposing one of an n-type semiconductor layer and a p-type semiconductorlayer adjacent to the light coupling structure. The light couplingstructure includes a Group III-V semiconductor material. An electrode isthen formed in the opening, the electrode in electrical communicationwith one of the n-type semiconductor layer and the p-type semiconductorlayer that is formed adjacent to an active layer. The active layer isformed adjacent to the other of the n-type semiconductor layer and thep-type semiconductor layer. The other of the n-type semiconductor layerand the p-type semiconductor layer is formed adjacent to the substrate.

In another embodiment, a method for forming a light emitting deviceincludes providing, in a reaction chamber, a substrate having a bufferlayer, and roughening a portion of the buffer layer to form a lightcoupling layer. The light coupling layer is formed adjacent to one of ann-type semiconductor layer and a p-type semiconductor layer that isformed adjacent to an active layer. The active layer is formed adjacentto the other of the n-type semiconductor layer and the p-typesemiconductor layer. The other of the n-type semiconductor layer and thep-type semiconductor layer is formed adjacent to the substrate.

In another embodiment, a method for forming a light emitting deviceincludes forming a buffer layer adjacent to a first substrate in areaction chamber and forming an n-type Group III-V semiconductor layeradjacent to the buffer layer. An active layer is formed adjacent to then-type Group III-V semiconductor layer, and a p-type Group III-Vsemiconductor layer is formed adjacent to the active layer. A secondsubstrate is then provided adjacent to the p-type Group III-Vsemiconductor layer. The first substrate is then removed to expose thebuffer layer. A light coupling layer is then formed from the bufferlayer. The light coupling layer includes an opening extending to then-type Group III-V semiconductor layer. An electrode is then provided inthe opening.

Additional aspects and advantages of the present disclosure will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein only illustrative embodiments of thepresent disclosure are shown and described. As will be realized, thepresent disclosure is capable of other and different embodiments, andits several details are capable of modifications in various obviousrespects, all without departing from the disclosure. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the features and advantages of the presentinvention will be obtained by reference to the following detaileddescription that sets forth illustrative embodiments, in which theprinciples of the invention are utilized, and the accompanying drawingsof which:

FIG. 1 schematically illustrates a light emitting diode;

FIG. 2 schematically illustrates a light emitting device having a lightcoupling layer, in accordance with an embodiment of the invention;

FIG. 3 schematically illustrates a light emitting device having a lightcoupling structure, in accordance with an embodiment of the invention;

FIG. 4 schematically illustrates a light emitting device, in accordancewith an embodiment of the invention;

FIG. 5 shows a method for forming a light emitting device, in accordancewith an embodiment of the invention;

FIGS. 6A-6L schematically illustrate a method for forming a lightcoupling layer and an electrode over an n-type gallium nitride layer, inaccordance with an embodiment of the invention; and

FIG. 7 shows a system for forming a light emitting device, in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION

While various embodiments of the invention have been shown and describedherein, it will be obvious to those skilled in the art that suchembodiments are provided by way of example only. Numerous variations,changes, and substitutions may occur to those skilled in the art withoutdeparting from the invention. It should be understood that variousalternatives to the embodiments of the invention described herein may beemployed in practicing the invention.

The term “light emitting device,” as used herein, refers to a deviceconfigured to generate light upon the recombination of electrons andholes in a light emitting region (or “active layer”) of the device, suchas upon the application (or flow) of a forward-biasing electricalcurrent through the light emitting region. A light emitting device insome cases is a solid state device that converts electrical energy tolight. A light emitting diode (“LED”) is a light emitting device. Thereare many different LED device structures that are made of differentmaterials and have different structures and perform in a variety ofways. Some light emitting devices emit laser light, and others generatenon-monochromatic light. Some LED's are optimized for performance inparticular applications. An LED may be a so-called blue LED including amultiple quantum well (MQW) active layer having indium gallium nitride.A blue LED may emit non-monochromatic light having a wavelength in arange from about 440 nanometers to 500 nanometers. A phosphor coatingmay be provided that absorbs some of the emitted blue light. Thephosphor in turn fluoresces to emit light of other wavelengths so thatthe light the overall LED device emits has a wider range of wavelengths.

The term “layer,” as used herein, refers to a layer of atoms ormolecules on a substrate. In some cases, a layer includes an epitaxiallayer or a plurality of epitaxial layers. A layer may include a film orthin film. In some situations, a layer is a structural component of adevice (e.g., light emitting diode) serving a predetermined devicefunction, such as, for example, an active layer that is configured togenerate (or emit) light. A layer generally has a thickness from aboutone monoatomic monolayer (ML) to tens of monolayers, hundreds ofmonolayers, thousands of monolayers, millions of monolayers, billions ofmonolayers, trillions of monolayers, or more. In an example, a layer isa multilayer structure having a thickness greater than one monoatomicmonolayer. In addition, a layer may include multiple material layers (orsub-layers). In an example, a multiple quantum well active layerincludes multiple well and barrier layers. A layer may include aplurality of sub-layers. For example, an active layer may include abarrier sub-layer and a well sub-layer.

The term “coverage,” as used herein, refers to the fraction of a surfacecovered or occupied by a species in relation the total area of thesurface. For example, a coverage of 10% for a species indicates that 10%of a surface is covered by the species. In some situations, coverage isrepresented by monolayers (ML), with 1 ML corresponding to completesaturation of a surface with a particular species. For example, a pitcoverage of 0.1 ML indicates that 10% of a surface is occupied by pits.

The term “active region” (or “active layer”), as used herein, refers toa light emitting region of a light emitting diode (LED) that isconfigured to generate light. An active layer includes an activematerial that generates light upon the recombination of electrons andholes with the aid of an electrical potential applied across the activelayer. An active layer may include one or a plurality of layers (orsub-layers). In some cases, an active layer includes one or more barrierlayers (or cladding layers, such as, e.g., GaN) and one or more quantumwell (“well”) layers (such as, e.g., InGaN). In an example, an activelayer includes multiple quantum wells, in which case the active layermay be referred to as a multiple quantum well (“MQW”) active layer.

The term “doped,” as used herein, refers to a structure or layer that ischemically doped. A layer may be doped with an n-type chemical dopant(also “n-doped” herein) or a p-type chemical dopant (also “p-doped”herein). In some cases, a layer is undoped or unintentionally doped(also “u-doped” or “u-type” herein). In an example, a u-GaN (or u-typeGaN) layer includes undoped or unintentionally doped GaN.

The term “adjacent” or “adjacent to,” as used herein, includes ‘nextto’, ‘adjoining’, ‘in contact with’, and ‘in proximity to’. In someinstances, adjacent to components are separated from one another by oneor more intervening layers. For example, the one or more interveninglayers can have a thickness less than about 10 micrometers (“microns”),1 micron, 500 nanometers (“nm”), 100 nm, 50 nm, 10 nm, 1 nm, or less. Inan example, a first layer is adjacent to a second layer when the firstlayer is in direct contact with the second layer. In another example, afirst layer is adjacent to a second layer when the first layer isseparated from the second layer by a third layer.

The term “substrate,” as used herein, refers to any workpiece on whichfilm or thin film formation is desired. A substrate includes, withoutlimitation, silicon, germanium, silica, sapphire, zinc oxide, carbon(e.g., graphene), SiC, AlN, GaN, spinel, coated silicon, silicon onoxide, silicon carbide on oxide, glass, gallium nitride, indium nitride,titanium dioxide and aluminum nitride, a ceramic material (e.g.,alumina, AlN), a metallic material (e.g., molybdenum, tungsten, copper,aluminum), and combinations (or alloys) thereof.

The term “Group III-V semiconductor,” as used herein, refers to amaterial having one or more Group III species (e.g., aluminum, gallium,indium) and one or more Group V species (e.g., nitrogen, phosphorous). AGroup III-V semiconductor material in some cases is selected fromgallium nitride (GaN), gallium arsenide (GaAs), aluminum galliumarsenide (AlGaAs), gallium arsenide phosphide (GaAsP), aluminum galliumindium phosphide (AlGaInP), gallium phosphide (GaP), indium galliumnitride (InGaN), aluminum gallium phosphide (AlGaP), aluminum nitride(AlN), aluminum gallium nitride (AlGaN), and aluminum gallium indiumnitride (AlGaInN).

The term “dopant,” as used herein, refers to a chemical dopant, such asan n-type dopant or a p-type dopant. P-type dopants include, withoutlimitation, magnesium, beryllium, zinc and carbon. N-type dopantsinclude, without limitation, silicon, germanium, tin, tellurium, andselenium. A p-type semiconductor is a semiconductor that is doped with ap-type dopant. An n-type semiconductor is a semiconductor that is dopedwith an n-type dopant. An n-type Group III-V material, such as n-typegallium nitride (“n-GaN”), includes a Group III-V material that is dopedwith an n-type dopant. A p-type Group III-V material, such as p-type GaN(“p-GaN”), includes a Group III-V material that is doped with a p-typedopant. A Group III-V material includes at least one Group III elementselected from boron, aluminum, gallium, indium, and thallium, and atleast one Group V element selected from nitrogen, phosphorus, arsenic,antimony and bismuth.

The term “injection efficiency,” as used herein, refers to theproportion of electrons passing through a light emitting device that areinjected into the active region of the light emitting device.

The term “internal quantum efficiency,” as used herein, refers to theproportion of all electron-hole recombination events in an active regionof a light emitting device that are radiative (i.e., producing photons).

The term “extraction efficiency,” as used herein, refers to theproportion of photons generated in an active region of a light emittingdevice that escape from the device.

The term “external quantum efficiency” (EQE), as used herein, refers tothe ratio of the number of photons emitted from an LED to the number ofelectrons passing through the LED. That is, EQE=Injection efficiency xInternal quantum efficiency×Extraction efficiency.

The term “light coupling structure,” as used herein, refers to astructure configured to permit light to transmit from a first medium toa second medium. The first medium has a fist index of refraction and thesecond medium has a second index of refraction that may be differentfrom the first index of refraction. A light coupling structure (orlayer) couples light from the first medium to the second medium.

The term “orifice,” as used herein, means opening or hole. An orifice,in some cases, is a cavity. An orifice includes an opening (such as avent, mouth, or hole) through which an object may pass. In someembodiments, an orifice is a recessed region. In some cases, an orificeis an etched-back region. An orifice can be filled with a material,including, but not limited to, a metallic or semiconductor material.

While silicon provides various advantages, such as the ability to usecommercially available semiconductor fabrication techniques adapted foruse with silicon, the formation of a Group III-V semiconductor-based LEDon a silicon substrate poses various limitations. As an example, thelattice mismatch and the mismatch in coefficient of thermal expansionbetween silicon and gallium nitride leads to structural stresses thatgenerate defects upon the formation of gallium nitride thin films, suchas dislocations.

LED's may be formed of various semiconductor device layers. In somesituations, Group III-V semiconductor LED's offer device parameters(e.g., wavelength of light, external quantum efficiency) that may bepreferable over other semiconductor materials. Gallium nitride (GaN) isa binary Group III-V direct bandgap semiconductor that may be used inoptoelectronic applications and high-power and high-frequency devices.

Group III-V semiconductor based LED's may be formed on varioussubstrates, such as silicon, germanium, sapphire, or silicon carbide(SiC). Silicon provides various advantages over other substrates, suchas the capability of using current manufacturing and processingtechniques, in addition to using large wafer sizes that aid inmaximizing the number of LED's formed within a predetermined period oftime. FIG. 1 shows an LED 100 having a substrate 105, an AlN layer 110adjacent to the substrate 105, an AlGaN layer 115 adjacent to the AlNlayer 110, an n-type GaN (“n-GaN”) layer 120 adjacent to the bufferlayer 115, an active layer 125 adjacent to the n-GaN layer 120, anelectron blocking (e.g., AlGaN) layer 130 adjacent to the active layer125, and a p-type GaN (“p-GaN”) layer 135 adjacent to the electronblocking layer 130. The electron blocking layer 130 is configured tominimize the recombination of electrons with holes in the p-GaN layer135. In some cases, the LED 100 includes a u-type GaN (“u-GaN”) layerbetween the AlGaN layer 115 and the n-GaN layer 120. The u-GaN layer mayprovide for enhanced coalescence between the AlGaN layer 115 and then-GaN layer 120. The substrate 100 may be formed of silicon. In somesituations, the LED 100 includes a substrate 140 (Substrate 2) adjacentto the p-GaN layer 135. In such a case, the substrate 105 may beprecluded. In some cases, the AlGaN layer 110 is part of the bufferlayer 115.

While silicon provides various advantages, the formation of Group III-Vsemiconductor based LED's on a silicon substrate poses variouslimitations. As an example, the lattice mismatch and mismatch incoefficient of thermal expansion between silicon and gallium nitride maygenerate structural stresses that may lead to high defect densities andcracking issues in LED devices. In an example, for an LED having a GaNepitaxial layer (also “epilayer” herein) on a silicon substrate, as theGaN epilayer gets thicker, the stress in the epilayer increases. Theincrease in stress may lead to the silicon wafer to bow and crack. Thecracking issue is more severe for a GaN layer that is n-doped withsilicon, due at least in part to a high tensile strain in silicon-dopedGaN. The thickness of the silicon-doped GaN layer may be selected toavoid cracking. The thickness limitation of Group III-V semiconductorlayers on silicon imposes various challenges to forming Group III-Vsemiconductor-based LED's with desirable performance characteristics.

In some cases, the extraction efficiency of LED devices may be improvedwith the aid of a light a coupling layer formed from a portion of ann-type semiconductor layer adjacent to an active layer of the LED. Thelight coupling layer couples light generated in the active layer of theLED from a first medium to a second medium, such as from a medium withinthe LED to an external environment. However, with the light couplinglayer formed from the n-type semiconductor layer, part of the n-typesemiconductor layer is sacrificed for optical extraction and,consequently, the effective n-type semiconductor layer thickness forcurrent spreading is reduced. In such a case, a thicker n-typesemiconductor layer may be necessary for both adequate roughening andcurrent spreading. However, the use of a thick n-type semiconductorlayer makes the growth of crack-free device layers difficult.

Structures and methods provided herein advantageously enable theformation of Group III-V semiconductor-based LED devices on silicon witha reduction in, if not an elimination of cracking, while providing fordevices with desirable performance characteristics (e.g., externalquantum efficiency). In some embodiments, a roughened u-type Group III-Vsemiconductor (e.g., u-GaN) layer over an n-type Group III-Vsemiconductor (e.g., n-GaN) layer is used as a light coupling layer (orlight coupling structure). In some situations, a roughened buffer layeris provided over (or adjacent to) the n-type Group III-V semiconductorlayer. The roughening of the n-type Group III-V semiconductor layer, insuch cases, may be reduced, if not eliminated, thereby providing foroptimized current spreading while advantageously enabling the use of arelatively thin Group III-V semiconductor layer, thereby aiding inavoiding cracking.

Light Emitting Devices with Light Coupling Layers

In an aspect of the invention, a light emitting device includes asubstrate, a p-type semiconductor layer adjacent to the substrate, anactive layer adjacent to the p-type semiconductor layer, and an n-typesemiconductor layer adjacent to the active layer. The light emittingdevice includes a light coupling structure adjacent to the n-type orp-type semiconductor layer. In some embodiments, at most a portion ofthe light coupling structure is formed from the n-type or p-typesemiconductor layer.

In some embodiments, the device further includes an electrode inelectrical communication with the n-type or p-type semiconductor layer.In some cases, the electrode is recessed in the light coupling layer.The electrode may be disposed in an orifice (or cavity) formed in thelight coupling layer. In an embodiment, the electrode is in contact (orelectrical contact) with the n-type or p-type semiconductor layer.

In some embodiments, the light coupling structure (or light couplinglayer) couples light from a first medium having a first refractive indexto a second having a second refractive index. The first and secondrefractive indexes may be different. In some cases, the secondrefractive index is less than the first refractive index.

During the operation of the light emitting device, at least some of thelight generated in the active layer is directed towards the lightcoupling structure, which scatters light at various angles, at leastsome of which may be directed out of the light emitting device. Thelight coupling structure may aid in directing light generated by theactive layer of the device.

In some embodiments, the light emitting device has an external quantumefficiency of at least about 40%, or at least about 50%, or at leastabout 60%, or at least about 65%, or at least about 70%, or at leastabout 75%, or at least about 80%, or at least about 85%, or at leastabout 90%, or at least about 95% at a drive current of about 350 mA.

In some situations, the light coupling structure has a corrugated orroughened surface. In some embodiments, the light coupling structure hasa first surface (e.g., top surface) opposite from a second surface(e.g., bottom surface). The first surface has a corrugation that isgreater than the corrugation of the second surface. The first surfacemay be in contact with the external environment, such as air or avacuum, or in contact with one or more layers, such as protectivelayers.

The n-type and/or p-type semiconductor layers may be formed of a GroupIII-V semiconductor material, such as gallium nitride. The substrate maybe formed of silicon. In embodiments, the thickness of the n-typesemiconductor layer is selected to minimize the stress imposed by thelattice mismatch and thermal mismatch between the silicon substrate andthe Group III-V semiconductor. In other cases, however, such as whendevice formation under induced stress conditions is desired, thethickness of the n-type semiconductor layer is selected to maintain apredetermined level of stress.

In some embodiments, a light emitting device includes a first layer of afirst type of Group III-V semiconductor material and a second layer of asecond type of Group III-V semiconductor material, and an active layerbetween the first layer and the second layer. The light emitting devicehas a light coupling layer adjacent to the second layer. The lightcoupling layer includes a third type of Group III-V semiconductormaterial. In some situations, the third type of Group III-Vsemiconductor material is different from the first type of Group III-Vsemiconductor material and the second type of Group III-V semiconductormaterial. An orifice (or cavity) formed in the light coupling layerextends through at least a portion of the light coupling layer towardsthe second layer. In some situations, the orifice extends through all orsubstantially all of the light coupling layer. An electrode formed inthe orifice provides an electrical flow path to the second layer.

In some embodiments, the orifice defines a channel in the light couplinglayer. The channel extends along some or all of the light couplinglayer. The electrode in such a case is formed in the channel and inelectrical communication with the second layer.

In some situations, the first type of Group III-V semiconductor materialis selected from one of an n-type Group III-V semiconductor and a p-typeGroup III-V semiconductor, and the second type of Group III-Vsemiconductor material is selected from the other of the n-type GroupIII-V semiconductor and the p-type Group III-V semiconductor. In anexample, the fist layer is formed of p-GaN and the second layer isformed of n-GaN. In some cases, the third type of Group III-Vsemiconductor material includes a u-type Group III-V semiconductormaterial, a doped Group III-V semiconductor material, and/or analuminum-containing Group III-V semiconductor material. In an example,the third type of Group III-V semiconductor material includes u-GaN(i.e., undoped or unintentionally doped GaN). In another example, thethird type of Group III-V semiconductor material includes n-GaN orp-GaN. In another example, the third type of Group III-V semiconductormaterial includes AlGaN or AlN.

In some cases, at most a portion of a light coupling layer is formedfrom an n-type or p-type Group III-V semiconductor layer adjacent to thelight coupling layer. In an example, an LED includes a substrate and afirst layer adjacent to the substrate. The first layer includes one of ap-type Group III-V semiconductor and an n-type Group III-Vsemiconductor. The LED includes a second layer adjacent to the firstlayer. The second layer includes an active material configured togenerate light upon the application of a forward-biasing electricalpotential across the second layer. The LED further includes a thirdlayer adjacent to the second layer. The third layer includes the otherof the p-type Group III-V semiconductor and the n-type Group III-Vsemiconductor. A light coupling structure is disposed adjacent to thethird layer. The light coupling structure includes one or more GroupIII-V semiconductor materials, such as one or more layers of Group III-Vsemiconductor materials. At most a portion of the light couplingstructure is formed from the third layer. In an embodiment, some of thelight coupling structure is formed from the third layer. In anotherembodiment, the light coupling structure is not formed from the thirdlayer.

The LED further includes an electrode formed adjacent to the thirdlayer. The electrode is in electrical communication with the thirdlayer. In some cases, the first layer has a p-type Group III-Vsemiconductor (e.g., p-GaN) and the third layer has an n-type GroupIII-V semiconductor (e.g., n-GaN).

The light coupling structure includes a fourth layer and a fifth layer,with the fourth layer being adjacent to the third layer of the LED. Insome embodiments, the fourth layer includes one or more of an n-typeGroup III-V semiconductor, u-type Group III-V semiconductor and analuminum-containing Group III-V semiconductor. In some cases, the fourthlayer includes one or more of n-type gallium nitride, u-type galliumnitride, aluminum gallium nitride and aluminum nitride. In someembodiments, the fifth layer includes one or more of a u-type GroupIII-V semiconductor and an aluminum-containing Group III-Vsemiconductor. In some cases, the fifth layer includes one or more ofu-type gallium nitride, aluminum gallium nitride and aluminum nitride.In an example, the fourth layer includes one or more of n-GaN, u-GaN,AlGaN and AlN, and the fifth layer includes one or more of u-GaN, AlGaNand AlN.

In some embodiments, the light coupling structure of the LED includes asixth layer adjacent to the fifth layer. In such a case, the fifth layeris between the fourth and sixth layers. In some embodiments, the sixthlayer includes an aluminum-containing Group III-V semiconductor. In somecases, the aluminum-containing Group III-V semiconductor is aluminumgallium nitride or aluminum nitride.

The light coupling structure includes an orifice extending across thelight coupling layer to the third layer. The orifice traverses thevarious layers of the light coupling structure, such as the fourth andfifth layers.

In an example, the light emitting device includes a silicon substrate, ap-GaN layer over the silicon substrate, an active layer over the p-GaNlayer, an n-GaN layer over the active layer, and a light coupling layerover the n-GaN layer. The light coupling layer includes AlGaN and/orAlN, and in some cases u-GaN. The light coupling layer in somesituations includes n-GaN. For instance, the light coupling layer mayinclude an n-GaN sub-layer adjacent to the n-GaN layer, a u-GaNsub-layer over the n-GaN sub-layer, and an AlGaN or AlN sub-layer overthe u-GaN sub-layer. As another example, the light coupling layer mayinclude an n-GaN sub-layer adjacent the n-GaN layer and an AlGaN or AlNsub-layer over the n-GaN sub-layer. The light coupling layer includes anorifice extending to the n-GaN layer. The device includes an electrodeformed in the orifice and in electrical contact with the n-GaN layer.The electrical contact in some situations is an ohmic contact.

The orifice of the light coupling layer may be a channel extending froma top surface of the light coupling layer through at least a portion ofthe light coupling layer. The channel also extends along a surface ofthe light coupling layer. In some cases, an electrode formed in theorifice is a line extending along at least a portion or substantiallyall of the orifice. The electrode is laterally bounded by the lightcoupling layer. In some situations, the electrode is recessed in thelight coupling layer. Alternatively, the orifice of the light couplinglayer is a via (or through hole) extending from the top surface of thelight coupling layer through at least a portion of the light couplinglayer. In some cases, the orifice extends through all or a substantialportion of the light coupling layer.

In some embodiments, n-type and p-type semiconductor layers are formedof a Group III-V semiconductor material. In an example, n-type andp-type semiconductor layers include gallium nitride. In such a case, then-type semiconductor layer includes gallium nitride and an n-typedopant, such as, e.g., silicon, and the p-type semiconductor layerincludes gallium nitride and a p-type dopant, such as, e.g., magnesium.

In some embodiments, light coupling structures are formed of variouscombinations of Group III-V materials. In some embodiments, a lightcoupling structure includes a first layer (or sub-layer) and a secondlayer adjacent to the first layer. In an example, the first layerincludes u-type GaN (u-GaN) and the second layer includes aluminumgallium nitride (AlGaN) or aluminum nitride (AlN).

In another example, the first layer includes AlGaN and the second layerincludes AlN. At least a portion of the light coupling layer may beformed of the n-type semiconductor layer. In another example, the firstlayer is formed of n-GaN and the second layer is formed of u-GaN, AlGaNor AlN. In some cases, the light coupling layer includes a third layerof a semiconductor material adjacent to the second layer. In an example,the third layer includes a Group III-V semiconductor material, such asAlGaN or AlN.

The light emitting device includes a first electrode in electricalcommunication with the n-type semiconductor layer and a second electrodein electrical communication with the p-type semiconductor layer. In somecases, the first electrode is adjacent to the light coupling layer andthe second electrode is adjacent to the substrate. The first electrodemay include one or more of titanium, aluminum, nickel, platinum, gold,silver, rhodium, copper and chromium. The second electrode may includeone or more of aluminum, titanium, chromium, platinum, nickel, gold,rhodium and silver. In some cases, the second electrode is formed of oneor more of platinum, nickel, silver, rhodium and gold.

In some embodiments, the first electrode covers a portion of the n-typesemiconductor layer. The shape and distribution of the first electrodemay be selected to minimize the obstruction of light emanating from thelight emitting device by the first electrode. In some cases, the firstelectrode is recessed in the light coupling layer.

The light coupling layer (or structure), in some cases, is a roughenedlayer, such as, e.g., a roughened layer of a buffer material. In anembodiment, the light coupling layer has a thickness between about 10 nmand 3 microns, or between about 100 nm and 2 microns, or between about200 nm and 1.5 microns. In another embodiment, the bottom portion (orfloor) of the orifice may have a corrugation that is between about 1 nmand 500 nm, or between about 10 nm and 100 nm.

In some embodiments, the light coupling layer is a roughened layer. Theroughened layer in some cases has protrusions. In some embodiments, thelight coupling layer has a roughness (or corrugation) that is betweenabout 10 nanometers (nm) and 3 micrometers (“microns”), or between about100 nm and 2 microns, or between about 200 nm and 1.5 microns. In otherembodiments, the light coupling layer has a corrugation that is greaterthan or equal to about 10 nm, or greater than or equal to about 50 nm,or greater than or equal to about 100 nm, or greater than or equal toabout 200 nm, or greater than or equal to about 300 nm, or greater thanor equal to about 400 nm, or greater than or equal to about 500 nm, orgreater than or equal to about 1000 nm.

In some embodiments, the light coupling layer has protrusions that havesizes (e.g., heights) between about 10 nanometers (nm) and 3 micrometers(“microns”), or between about 100 nm and 2 microns, or between about 200nm and 1.5 microns. In other embodiments, the light coupling layer hasprotrusions that have sizes greater than or equal to about 10 nm, orgreater than or equal to about 50 nm, or greater than or equal to about100 nm, or greater than or equal to about 200 nm, or greater than orequal to about 300 nm, or greater than or equal to about 400 nm, orgreater than or equal to about 500 nm, or greater than or equal to about1000 nm.

The orifice (or cavity) exposes a portion of the light coupling layer ora layer below the light coupling layer, such as the n-type semiconductorlayer. In some cases, the exposed portion has a corrugation that is lessthan the corrugation of the light coupling layer. In some embodiments,the exposed portion has a corrugation that is less than or equal toabout 500 nanometers (nm), or less than or equal to about 300 nm, orless than or equal to about 200 nm, or less than or equal to about 100nm. The exposed portion may have a corrugation that is between about 1nm and 500 nm, or between about 10 nm and 100 nm.

The corrugation, or surface roughness, of the light coupling layer and arecessed surface of the orifice (i.e., bottom portion of the orifice)may be measured with the aid of various surface spectroscopic tools,such as scanning tunneling microscopy (STM), atomic force microscopy(AFM) or various surface scattering techniques, such as Ramanspectroscopy. The corrugation may correspond to the height (e.g.,pit-to-peak distance) of a moiety of the light coupling layer.

In some cases, the orifice includes one or more sidewalls and a floor.In some situations, the orifice is box-like or rectangular. In othercases, the orifice is semi-circular or semi-elliptical. In such cases,the orifice may not have a floor. The orifice may be a line having afirst dimension (along a surface of the light coupling layer) that islonger than a second dimension perpendicular to the first dimension.Alternatively, the first and second dimensions may be substantially thesame. The orifice in such a case may be a via-type structure.

In some cases, the light coupling layer includes one or more lightcoupling moieties disposed at a surface of the light coupling layer. Insome embodiments, the light coupling moieties are protrusions. The lightcoupling moieties may be formed of a diffuse optically transmittingmaterial. In some embodiments, an individual moiety of the lightcoupling moieties may be two-dimensional or three-dimensional, such as athree-dimensional cone or horn, or a line having a two-dimensionalgeometric cross-section. An individual light coupling moiety may have adecreasing width along an axis oriented away from the active layer. Inan embodiment, an individual light coupling moiety has a triangularcross-section. In another embodiment, an individual light couplingmoiety is pyramidal or substantially pyramidal. In other cases, anindividual light coupling moiety has a substantially constant widthalong an axis oriented away from the active layer. In an embodiment, anindividual light coupling moiety has a cross-section that is square orrectangular. In an example, an individual light coupling moiety isrod-like. The corrugation at the surface of the light coupling layer maybe selected to optimize the coupling of light from a first medium to asecond medium. The first medium may be internal to the light emittingdevice and the second medium may be external to the light emittingdevice.

In some embodiments, the substrate includes one or more of silicon,germanium, silicon oxide, silicon dioxide, titanium oxide, titaniumdioxide and sapphire, silicon carbide, alumina, aluminum nitride,copper, tungsten, molybdenum, and combinations thereof. In a particularimplementation, the substrate is silicon, such as, e.g., p-type silicon.

In some situations, the light emitting device further includes anoptical reflector between the substrate and the p-type semiconductorlayer. The optical reflector may be formed of one or more of silver,platinum, gold and nickel, rhodium and indium.

In some embodiments, the active layer includes an active material havinga Group III-V semiconductor. In some cases, the active material is aquantum well active material, such as a multiple quantum well (MQW)material. In an embodiment, the active layer includes alternating welllayers (or sub-layers) and barrier (or cladding) layers. In an example,the active layer includes a well layer formed of indium gallium nitrideand/or indium aluminum gallium nitride. In such a case, the barrierlayer may be formed of gallium nitride. In another example, the activelayer includes a well layer formed of aluminum gallium nitride. In sucha case, the barrier layer may be formed of aluminum nitride or galliumnitride. The active material of the active layer may be compositionallygraded (also “graded” herein) in two or more elements. In an example,the active layer includes graded indium gallium nitride,In_(x)Ga_(1-x)N, wherein ‘x’ is a number between 0 and 1, and a barrier(or cladding) layer formed of GaN. The composition of such a layer mayvary from a first side to a second side of the active layer. In somesituations, a well layer includes an acceptor material and/or a barrierlayer includes a donor material. In some embodiments, barrier materialsinclude one or more of gallium nitride, indium gallium nitride andaluminum nitride, and well materials include one or more of indiumgallium nitride, indium aluminum gallium nitride.

As an alternative, the active layer is formed of AlGaInP. In some cases,an AlGaInP-containing quantum well active layer includes one or morewell layers formed of AlGaInP and one or more barrier layers formed ofAlInP.

In other embodiments, a light emitting device includes a light couplingstructure adjacent to a p-type semiconductor layer. In an example, alight emitting device includes a substrate, a first layer having ann-type Group III-V semiconductor adjacent to the substrate, an activelayer adjacent to the first layer, a second layer having a p-type GroupIII-V semiconductor adjacent to the active layer, and a light couplingstructure adjacent to the second layer. The n-type and p-type GroupIII-V semiconductors may be formed of gallium nitride. The substrate maybe formed of silicon. The light coupling structure may include a singlelayer or a plurality of layers.

The light coupling structure includes an orifice extending at leastpartly through the light coupling structure. In some situations, theorifice (e.g., channel) extends through all of the light couplingstructure. The light emitting device includes a first electrode inelectrical communication with the second layer, such as by directcontact with the second layer or by way of a doped layer between theelectrode and the second layer. The orifice in other cases extendsthrough the light coupling structure to a top surface of the secondlayer. The orifice in such a case is defined in part by the top surfaceof the second layer. The light emitting device includes a secondelectrode in electrical communication with the first layer.

FIG. 2 shows a light emitting device 200, in accordance with anembodiment of the invention. The device 200 may be a light emittingdiode (LED), such as a vertically stacked LED. The device 200 includes,from bottom to top, a bottom electrode 205, a substrate 210, anoptically reflective layer 215, a p-type semiconductor layer 220, anactive layer 225, an n-type semiconductor layer 230, a light couplinglayer 235, and a top electrode 240. The arrows in the device 200indicate the direction of the flow of current upon the application of anelectrical potential across the electrodes 205 and 240. The topelectrode 240 is formed in an orifice 245 formed in the light couplinglayer 235. The electrode 240 is in contact with the n-type semiconductorlayer 230 at a surface 250 of the n-type semiconductor layer 230.

The active layer 225 may be a quantum well active layer having a welllayer and a barrier layer, or a multiple quantum well (MQW) active layerhaving a plurality of well layers and barrier layers. In an example, theactive layer 225 is formed of alternating GaN barrier layers and indiumgallium nitride or aluminum indium gallium nitride well layers. Theactive layer 225 is configured to generate light upon the recombinationof electrons and holes in the active layer 225.

The light coupling layer 235 is configured to couple light generated inthe device 200 and emanating from the n-type semiconductor layer 230 toan environment outside the device 200 or to another layer over the lightcoupling layer 235. In an embodiment, the light coupling layer 235facilitates the transmission of light from the n-type semiconductor 230layer having a first refractive index to a material or environmenthaving a second refractive index that is lower than the first refractiveindex.

The optically reflective layer 215 is formed of a material configured toreflect light generated in the active layer 225 towards the lightcoupling layer 235. With the aid of the optically reflective layer 215,light that is initially generated in the active layer 225 and directedtoward the substrate 210 is reflected by the optically reflective layer215 towards the active layer 225 and the light coupling layer 235. Insome cases, the optically reflective layer 215 is formed of a reflectivep-type electrode. In other cases, the optically reflective layer isformed of silver, platinum, gold, nickel, aluminum, rhodium and indium.In some situations, the optically reflective layer 215 is anomnidirectional reflector

The device 200 may include one or more additional layers. For instance,the device 200 may include a pit generation layer between the n-typesemiconductor layer 230 and the active layer 225 configured tofacilitate the formation of V-pits (or V-defects) in the active layer225. In an embodiment, the device 200 includes an electron blockinglayer between the p-type semiconductor layer 220 and the active layer225, which is configured to minimize electron-hole recombination in thep-type semiconductor layer 220.

In some situations, the n-type semiconductor layer 230 is formed of ann-type Group III-V semiconductor, such as n-type gallium nitride. Insome cases, The p-type semiconductor layer 220 is formed of a p-typeGroup III-V semiconductor, such as p-type gallium nitride. In anexample, the n-type semiconductor layer 230 is doped n-type with the aidof silicon. In another example, the p-type semiconductor layer 220 isdoped p-type with the aid of magnesium.

In some embodiments, the light coupling layer 235 is formed of one ormore semiconductor materials. In some situations, the light couplinglayer 235 is formed of buffer layer material. The light coupling layer235 may be compositionally graded between a first type of semiconductormaterial and a second type of semiconductor material, such as between afirst type of Group III-V semiconductor and a second type of Group III-Vsemiconductor. Alternatively, the light coupling layer 235 includes oneor more discrete layers that are not compositionally graded.

In some situations, the light coupling layer (or structure) 235 includesa plurality of sub-layers (or layers) having materials generally of theformula M1_(x)M2_(1-x)C_(y), wherein ‘M1’ and ‘M2’ are Group IIImaterials, and ‘C’ is a Group V material. In some cases, the lightcoupling layer 235 includes a plurality of layers selected fromAl_(x)Ga_(1-x)N, wherein ‘x’ is a number between 0 and 1. For instance,the light coupling layer 235 may include one or more materials selectedfrom AlN, AlGaN and u-type GaN. In an example, the light coupling layer235 includes a u-type GaN layer (i.e., a layer having u-GaN) and anAlGaN layer (i.e., a layer having AlGaN). In another example, the lightcoupling layer 235 includes a u-type GaN layer, an AlGaN layer, and anAlN layer (i.e., a layer having AlN). In another example, the lightcoupling layer 235 includes an n-GaN layer, an AlGaN layer and an AlNlayer. In another example, the light coupling layer 235 includes ann-GaN layer and an AlGaN layer. The light coupling layer 235 may alsoinclude an AlN layer. In another example, the light coupling layer 235includes a u-GaN layer and an AlGaN layer. The light coupling layer 235may also include an AlN layer. The u-GaN layer in some cases isoptional.

In some situations, the light coupling layer 235 is formed of a u-typesemiconductor material. In an embodiment, the light coupling layer 235is formed of a u-type Group III-V semiconductor, such as u-type galliumnitride (u-GaN). The light coupling layer 235 may include a layer of asemiconductor material, such as a Group III-V semiconductor material(e.g., AlGaN), over the u-type semiconductor material. In someembodiments, the light coupling layer 235 includes a layer of an n-typesemiconductor material (e.g., n-GaN) and a layer of the u-typesemiconductor material. The layer of the n-type semiconductor materialmay be formed from a portion of the n-type Group III-V semiconductorlayer 230.

In some situations, the light coupling layer 235 is formed from analuminum-containing Group III-V semiconductor material (e.g., AlGaN). Insome situations, the light coupling layer 235 includes an additionallayer of a Group III-V semiconductor. In an example, the light couplinglayer includes a layer of AlGaN and a layer of AlN. The layer of AlGaNis disposed adjacent to the n-type semiconductor layer 230. In someembodiments, the light coupling layer 235 includes a layer of an n-typesemiconductor material and one or more aluminum-containing layersadjacent to the layer of the n-type semiconductor material, such as anAlGaN layer and/or an AlN layer. The layer of the n-type semiconductormaterial, in some cases, is formed from a portion of the n-type GroupIII-V semiconductor layer 230. The light coupling layer 235 may includea layer of a u-type Group III-V semiconductor, such as u-GaN, betweenthe n-type semiconductor layer 230 and the one or morealuminum-containing layers.

The bottom electrode 205 is formed adjacent to the substrate 210. Thebottom electrode 205 is in electrical communication with the p-typesemiconductor layer 220 through the substrate and the opticallyreflective layer 215. In some situations, the device 200 includes one ormore additional layers between the bottom electrode 205 and thesubstrate 210.

The top electrode 240 is formed in the orifice 245. The top electrode240 is in electrical communication with the n-type semiconductor layer230. As illustrated, the top electrode 240 is in contact with the n-typesemiconductor layer 230. The contact in some cases is an ohmic contact.In some situations, the device 200 includes one or more additionallayers between the top electrode 240 and the n-type semiconductor layer230.

Alternatively, the p-type semiconductor layer 220 and the n-typesemiconductor layer 230 are reversed. That is, the light coupling layer235 is adjacent to the p-type semiconductor layer and the n-typesemiconductor layer is disposed between the substrate 210 and the activelayer 225.

FIG. 3 shows a light emitting device 300, in accordance with anembodiment of the invention. The device 300 includes, from bottom totop, a semiconductor layer 305, a light coupling layer (or structure)310 and an electrode 315. The light coupling layer 310 includes a firstlayer (or sub-layer) 320 and a second layer (or sub-layer) 325. Thelight coupling layer 310 includes light coupling moieties 330. Theelectrode 315 is formed in a cavity (or opening) 335 of the lightcoupling layer 310. The electrode 315 is in contact with thesemiconductor layer 305.

In an embodiment, the semiconductor layer 305 is formed of an n-typesemiconductor. In another embodiment, the semiconductor layer 305 isformed of a p-type semiconductor. In some cases, the semiconductor layer305 is formed of an n-type or p-type Group III-V semiconductor. In anexample, the semiconductor layer 305 is formed of n-GaN.

The first layer 320 is formed of a semiconductor material. In somesituations, the first layer is formed of an n-type or p-typesemiconductor material. The first layer 320 may be formed of a GroupIII-V semiconductor. As an example, the first layer is formed of n-GaN.As another example, the first layer 320 is formed of u-type GaN. Asanother example, the first layer 320 is formed of p-GaN. As anotherexample, the first layer 320 is formed of an aluminum-containing GroupIII-V semiconductor material, such as AlGaN. In an embodiment, the firstlayer 320 is formed of a portion of the semiconductor layer 305.

In some embodiments, the second layer 325 is formed of a semiconductormaterial. In some situations, the second layer 325 is formed of a GroupIII-V semiconductor. In an example, the second layer 325 is formed ofgallium nitride, such as u-type GaN. In another example, the secondlayer 325 is formed of an aluminum-containing Group III-V semiconductor,such as aluminum gallium nitride or aluminum nitride.

The light coupling structure 310 may include a third layer adjacent tothe second layer 325. The third layer may include a Group III-Vsemiconductor, such as an aluminum-containing Group III-V semiconductor(e.g., AlGaN or AlN).

The electrode 315 is formed of one or more elemental metals. In someembodiments, the electrode 315 is formed of one or more of titanium,aluminum, nickel, platinum, gold, silver, rhodium, copper and chromium.

In some embodiments, the first layer 320 is formed of a first type ofGroup III-V semiconductor and the second layer 325 is formed of a secondtype of Group III-V semiconductor.

In some situations, the light coupling layer 310 is formed of a singlelayer of a Group III-V semiconductor, such as a single layer of a u-typeGroup III-V semiconductor, an n-type or p-type Group III-Vsemiconductor, or an aluminum-containing Group III-V semiconductor.

In an example, the first layer 320 is formed of u-GaN and the secondlayer 325 is formed of AlGaN or AlN. In some cases, the light couplinglayer 310 includes a third layer over the second layer 325. The thirdlayer may be formed of AlGaN or AlN. As another example, the first layer320 is formed of n-GaN (e.g., silicon-doped GaN) and the second layer325 is formed of u-GaN, AlGaN or AlN. Such a configuration may be usedin cases in which the semiconductor layer 305 is formed of n-GaN, suchas silicon doped GaN. As another example, the first layer 320 is formedof n-GaN and the second layer 325 is formed of AlGaN, and the thirdlayer (not shown) is formed of AlN. As another example, the first layer320 is formed of n-GaN; the second layer 325 is formed of one of u-GaN,AlGaN and AlN; and the third layer is formed of the other of u-GaN,AlGaN and AlN. As another example, the light coupling layer 310 isformed of a single layer having u-GaN, AlGaN or AlN.

In some situations, the light coupling layer 310 is formed of a bufferlayer material used to form the device 300. The buffer layer material,in some cases, includes one or more Group III-V semiconductor materials,such as one or more of u-GaN, AlGaN and AlN. The light coupling layer310 may be formed by roughening a buffer layer from previous processingoperations (see below).

The light coupling layer 310 may be formed of 1, or 2, or 3, or 4, or 5,or 6, or 7, or 8, or 9, or 10, or more layers. For example, the lightcoupling layer 310 includes a u-GaN, aluminum gallium nitride (AlGaN),or aluminum nitride (AlN) layer and no other layers. As another example,the light coupling layer 310 is formed of a u-GaN layer and an AlGaN (orAlN) layer. As another example, the light coupling layer 310 is formedof an n-GaN layer and a u-GaN, AlGaN or AlN layer. As another example,the light coupling layer 310 is formed of an AlGaN layer and an AlNlayer. As another example, the light coupling layer 310 is formed of ann-GaN layer, an AlGaN layer and an AlN layer. The light coupling layer310 may include an optional u-GaN layer.

In some embodiments, the light coupling moieties 330 are two-dimensionalor three-dimensional. In some situations, the light coupling moieties330 are lines (e.g., directed into the plane of the page) withtriangular cross-sections. Alternatively, the light coupling moieties330 may have square or rectangular cross-sections. In other situations,the light coupling moieties 330 are three-dimensional. In such a case,the light coupling moieties 330 may be cone-like or pyramidal.Alternatively, the light coupling moieties 330 may be rod-like.

In some embodiments, the device 300 includes one or more additionallayers. In an example, the device 300 includes an active layer below thesemiconductor layer 305, and another semiconductor layer 305 below theactive layer. The active layer is configured to generate light upon therecombination of electrons and holes in the active layer. Some of thelight generated in the active layer is directed toward the lightcoupling layer 310, which scatters light at various angles, at leastsome of which may be directed out of the device 300. The light couplinglayer 310 may therefore increase the fraction of light generated by thedevice 300 that is directed out of the device.

In some embodiments, the light coupling layer 310 has a corrugationbetween about 10 nm and 3 microns, or between about 100 nm and 2microns, or between about 200 nm and 1.5 microns. In some cases, thelight coupling layer 310 has a corrugation that is less than 0.5microns. The corrugation corresponds to the distance between the highestpoint of an individual moiety and the lowest point of the individualmoiety, as illustrated by “D” in FIG. 3. The electrode 315 has a height(H) that is greater than D. In other cases, the electrode 315 has aheight that is less than or equal to D.

The electrode 315 is disposed in the cavity (or orifice) 335 and incontact with the semiconductor layer 305 at the surface 340 of thesemiconductor layer 305. Such a configuration provides an electric flowpath from semiconductor layer 305 to the electrode 315. The contactbetween the electrode 315 and the semiconductor layer 305 may be ohmic,which helps maximize the extraction efficiency of electrons from thedevice 300.

In some embodiments, the bottom portion (or floor) 340 of the orifice335 has a corrugation that is between about 1 nm and 500 nm, or betweenabout 10 nm and 100 nm. In some cases, the corrugation of the bottomportion 340 is less than about 0.5 microns, or 0.1 microns, or 0.01microns. The corrugation of the bottom portion 340 is smaller than thecorrugation of the light coupling layer 310.

In some embodiments, the light coupling layer 310 couples light from afirst medium having a first refractive index to a second medium having asecond refractive index. In an embodiment, the light coupling layer 310(including the light coupling moieties 330) couples light from a mediuminternal to the device 300, such as the semiconductor layer 305, to amedium above the light coupling layer 310 (such as, e.g., external tothe device 300).

In an example, a light emitting device includes a Group III-Vsemiconductor over a silicon substrate. FIG. 4 shows a light emittingdevice 400, having, from bottom to top, a contact layer 405, a substrate410, a reflective layer 415, a p-type Group III-V semiconductor layer420, an active layer 425, an n-type Group III-V semiconductor layer 430,a light coupling layer 435, and an electrode 440, in accordance with anembodiment of the invention. The contact layer 405 may be for providingan electrical contact between the device 400 and a package substrate,such as a transistor outline (TO) header or a metal core printed circuitboard (MCPCB). The light coupling layer 435 includes a portion of thematerial of the n-type Group III-V semiconductor layer 430. In somecases, however, the light coupling layer 435 does not include a portionof the material of the n-type semiconductor layer 430. The electrode maybe formed of a reflective n-type electrode. The electrode 440 isrecessed in the light coupling layer 435. In some situations, theelectrode 440 is formed in an orifice (or cavity) formed in the lightcoupling layer 435. The electrode 440 is in electrical communicationwith the n-type Group III-V semiconductor layer 430. In some cases, theelectrode 440 is in ohmic contact with the n-type Group III-Vsemiconductor layer.

The substrate 410 may be formed of silicon, germanium, silicon oxide,silicon dioxide, titanium oxide, titanium dioxide or sapphire. In somecases, the substrate 410 is formed of silicon, germanium, or othersemiconductor, a ceramic (e.g., Al₂O₃, aluminum nitride, magnesiumoxide) material, or a metal (e.g., molybdenum, tungsten, copper,aluminum).

The reflective layer 415 is formed of a material configured to reflectlight. In an embodiment, the reflective layer 415 is formed of silver.

The p-type Group III-V semiconductor layer 420, in some cases, is formedof p-type GaN. In an embodiment, p-type doping is achieved with the aidof magnesium, though other p-type dopants may be used as required toachieve desired device performance. The p-type Group III-V semiconductorlayer 420 has a thickness between about 10 nanometers (nm) and 1000 nm,or between about 50 nm and 500 nm.

The active layer 425 may be a quantum well active layer. In someembodiments, the active layer 425 is a multiple quantum well activelayer including a plurality of alternating well layers and barrierlayers. In some situations, the active layer 425 includes GaN barrierlayers and aluminum indium gallium nitride or indium gallium nitridewell layers.

In some embodiments, the n-type Group III-V semiconductor layer 430 isformed of n-type GaN. In an embodiment, n-type doping is achieved withthe aid of silicon, though other n-type dopants may be used as requiredto achieve desired device performance. The n-type Group III-Vsemiconductor layer 430 has a thickness between about 500 nm and 5micrometers (“microns”), or between about 1 micron and 3 microns. Insome cases, the n-type Group III-V semiconductor layer 430 has athickness less than or equal to about 5 microns, or less than or equalto about 4 microns, or less than or equal to about 3 microns, or lessthan or equal to about 2 microns, or less than or equal to about 1micron.

In some embodiments, the light coupling layer 435 has a corrugationbetween about 10 nm and 3 microns, or between about 100 nm and 2microns, or between about 200 nm and 1.5 microns. The corrugation may beselected to achieve desired device performance. The electrode 440 isdisposed on a surface of the n-type Group III-V semiconductor layer 430.The corrugation of the surface is between about 1 nm and 500 nm, orbetween about 10 nm and 100 nm.

In some situations, the contact layer 405 is in electrical communicationwith the substrate 410 and the p-type Group III-V semiconductor layer420. The contact layer 405 may be in ohmic contact with the substrate410. The device 400 includes another electrode that is in electricalcommunication with the n-type Group III-V semiconductor layer 430. Theother electrode may be provided through a hole or via extending from atop surface (at or adjacent to the light coupling layer 435) to then-type group III-V semiconductor layer 430.

The light coupling layer 435, as illustrated, is formed of a layer ofaluminum gallium nitride or aluminum nitride. In some situations, thelight coupling layer 435 includes a u-GaN layer in addition to an AlGaNor AlN layer. In some cases, the light coupling layer 435 includes au-GaN layer between the n-type Group III-V semiconductor layer 430 andthe AlGaN or AlN layer.

In an example, the light coupling layer 435 is formed of an AlGaN layer.In another example, the light coupling layer 435 is formed of an AlNlayer. In another example, the light coupling layer 435 is formed of anAlGaN layer over the n-type Group III-V semiconductor layer 430 and anAlN layer over the AlGaN layer. In another example, the light couplinglayer 435 is formed of a u-GaN layer over the n-type Group III-Vsemiconductor layer 430 and an AlGaN layer over the u-GaN layer. In sucha case, the light coupling layer 435 may include an AlN layer over theAlGaN layer.

Methods for Forming Light Coupling Layers

In another aspect of the invention, methods for forming light couplinglayers (or structures) are provided. Methods provided herein may be usedto form light coupling devices for use with light emitting devices, suchas light emitting diodes (LED's). In a particular implementation,methods provided herein are used to form light coupling layers for usewith LED's having Group III-V semiconductors on silicon substrates.

In some embodiments, a method for forming a light emitting deviceincludes providing a substrate in a reaction chamber and forming one ormore device layers on the substrate. In some situations, the lightemitting device is formed on a substrate that will be included in theend product light emitting device. In other situations, the substrate isa carrier substrate, and a stack of device structures formed on thesubstrate will be transferred to another substrate that will be includedin the end product. The carrier substrate in such a case will not beincluded in the end product. In some embodiments, the substrate includesone or more of silicon, germanium, silicon oxide, silicon dioxide,titanium oxide, titanium dioxide, SiC and sapphire. In a particularimplementation, the substrate is silicon, such as n-type silicon.

The reaction chamber may be a vacuum chamber configured for thin filmformation. The vacuum chamber, in some cases, is an ultrahigh vacuum(UHV) chamber. In cases in which a low-pressure environment is desired,the reaction chamber may be pumped with the aid of a pumping systemhaving one or more vacuum pumps, such as one or more of a turbomolecular(“turbo”) pump and a diffusion pump and a mechanical pump. The reactionchamber may include a control system for regulating precursor flowrates, substrate temperature, chamber pressure, and the evacuation ofthe chamber.

Growth conditions are adjustable based upon the selection of one or moreprocess parameters for forming the light emitting device. In someembodiments, growth conditions are selected from one or more of growthtemperature, carrier gas flow rate, precursor flow rate, growth rate andgrowth pressure.

Various source gases (or precursors) may be used with methods describedherein. A gallium precursor may include one or more of trimethylgallium(TMG), triethylgallium, diethylgallium chloride and coordinated galliumhydride compounds (e.g., dimethylgallium hydride). An aluminum precursormay include one or more of tri-isobutyl aluminum (TIBAL), trimethylaluminum (TMA), triethyl aluminum (TEA), and dimethylaluminum hydride(DMAH). An indium precursor may include one or more of trimethyl indium(TMI) and triethyl indium (TEI). A nitrogen precursor may include one ormore of ammonia (NH₃), nitrogen (N₂), and plasma-excited species ofammonia and/or N₂. A p-type dopant precursor may include one or more ofa boron precursor (e.g., B₂H₆), a magnesium precursor (e.g.,biscyclopentadienyl magnesium), an aluminum precursor, to name a fewexamples. An n-type precursor may include one or more of a siliconprecursor (e.g, SiH₄), a germanium precursor (e.g.,tetramethylgermanium, tetraethylgermanium, dimethyl amino germaniumtetrachloride, isobutylgermane) and a phosphorous precursor (e.g., PH₃),to name a few examples.

In some cases, one or more precursor are provided to a reaction chamberwith the aid of a carrier gas including one or more of He, Ar, N₂ andH₂. In an embodiment, the flow rate of the carrier gas during theformation of the active layer is between about 1 liter/minute and 20liters/minute.

FIG. 5 shows a method 500 for forming a light emitting device, inaccordance with some embodiments of the invention. In some cases, thefirst substrate is selected from silicon, germanium, silicon oxide,silicon dioxide, titanium oxide, titanium dioxide, sapphire, siliconcarbide (SiC), a ceramic material (e.g., alumina, AlN) and a metallicmaterial (e.g., molybdenum, tungsten, copper, aluminum). In animplementation, the first substrate is silicon.

In a first operation 505, with the first substrate provided in thereaction chamber, a buffer layer is formed adjacent to the firstsubstrate. The buffer layer is formed by directing into the reactionchamber one or more precursors of the buffer layer and exposing thesubstrate to the one or more precursors. In some embodiments, the bufferlayer is formed of a Group III-V semiconductor material. In somesituations, the buffer layer is formed of a stack having an AlGaN layerand an AlN layer, with the AlN layer being directly adjacent to thefirst substrate. In such a case, the AlN layer is formed by directinginto the reaction chamber an aluminum precursor and a nitrogenprecursor, and the AlGaN layer is formed by directing into the reactionchamber an aluminum precursor, a gallium precursor and a nitrogenprecursor. The aluminum precursor may be TMA, the gallium precursor maybe TMG, and the nitrogen precursor may be NH₃. In some cases, the bufferlayer includes a u-GaN layer adjacent to the AlGaN layer. The u-GaNlayer may be formed by directing into the reaction chamber a galliumprecursor and a nitrogen precursor.

Next, in operation 510, an n-type Group III-V semiconductor layer isformed adjacent to the buffer layer. The n-type Group III-Vsemiconductor layer is formed by directing a Group III precursor, aGroup V precursor and the precursor of an n-type dopant into thereaction chamber. In an example, with the n-type Group III-Vsemiconductor layer including n-GaN, the n-GaN layer is formed bydirecting a gallium precursor, a nitrogen precursor and the precursor ofthe n-type dopant into the reaction chamber. In cases in which then-type dopant is silicon, the precursor of the n-type dopant may besilane (SiH₄).

Next, in operation 515, an active layer is formed adjacent to the n-typeGroup III-V semiconductor layer. In some embodiments, the active layerincludes a quantum well material, such as multiple quantum well (MQW)material. The active layer is formed by forming one or more well layersthat alternate with one or more barrier layers. In an example, theactive layer includes GaN (or AlN) barrier layers and indium galliumnitride or aluminum indium gallium nitride well layers. In such a case,the active layer is formed by directing into the reaction chamber agallium (or aluminum) precursor and a nitrogen precursor to form abarrier layer, and subsequently directing an indium precursor, galliumprecursor and nitrogen precursor (and aluminum precursor, if an aluminumindium gallium nitride well layer is desired) into the reaction chamberto form a well layer. Such operations may be repeated as desired to forman active layer with a predetermined number of barrier layer and welllayer stacks (or periods). In an example, the operations are repeateduntil an active layer having at least 1, or at least 10, or at least 20,or at least 50, or at least 100 periods is formed.

Next, in operation 520, a p-type Group III-V semiconductor layer isformed adjacent to the active layer. The p-type Group III-Vsemiconductor layer is formed by directing a Group III precursor, aGroup V precursor and the precursor of a p-type dopant into the reactionchamber. In an example, with the p-type Group III-V semiconductor layerincluding p-GaN, the p-GaN layer is formed by directing a galliumprecursor, a nitrogen precursor and the precursor of the p-type dopant(e.g., biscyclopentadienyl magnesium for a magnesium dopant) into thereaction chamber. In some cases, following the formation of the p-typeGroup III-V semiconductor layer, a layer of a reflective material (e.g.,Ag) is formed on the p-type Group III-V semiconductor layer. Aprotective metal layer may then be formed over the layer of thereflective material. In some cases, the protective metal layer includesone or more of gold, platinum, titanium, tungsten, nickel. Theprotective metal layer may be formed with the aid of various depositiontechniques, such as physical vapor deposition (e.g., magnetronsputtering).

Next, in operation 525, a second substrate is provided adjacent to thep-type Group III-V semiconductor layer. In some cases, the secondsubstrate is selected from silicon, germanium, silicon oxide, silicondioxide, titanium oxide, titanium dioxide, sapphire, silicon carbide(SiC), a ceramic material (e.g., alumina, AlN) and a metallic material(e.g., molybdenum, tungsten, copper, aluminum). In some situations, thesecond substrate is provided adjacent to the p-type Group III-Vsemiconductor layer by bringing the second substrate in contact with thep-type Group III-V semiconductor layer. In other cases, the secondsubstrate has formed thereon a layer of a metallic material to aid inbonding the second substrate to the nascent light emitting diode (i.e.,the device stack including the p-type Group III-V semiconductor layerover the first substrate). In an embodiment, the metallic materialincludes one or more metals selected from indium, copper, silver goldand tin, such as, e.g., a silver tin copper alloy or a gold tin alloy(e.g., 80% gold, 20% tin). The layer of the metallic material may beformed with the aid of various deposition techniques, such as physicalvapor deposition (e.g., magnetron sputtering, evaporative deposition).Next, in operation 530, the first substrate is removed to expose thebuffer layer.

Next, in operation 535, a light coupling layer is formed from the bufferlayer and, in some cases, the n-type Group III-V semiconductor layer.The light coupling layer, as formed, has an opening (or orifice)extending through at least a portion of the buffer layer. In someembodiments, the light coupling layer is formed by roughening the bufferlayer.

Next, in operation 540, an electrode is provided in the opening. In anembodiment, the electrode is formed with the aid of a physical vapordeposition technique, such as sputtering. The electrode is in electricalcommunication with the n-type Group III-V semiconductor layer. In anexample, the electrode is in electrical contact with the n-type GroupIII-V semiconductor layer.

In some cases, at least a portion of the n-type Group III-Vsemiconductor layer is roughened, while the remainder (such as theportion of the n-type Group III-V semiconductor layer in the orifice) isnot roughened.

During one or more of the operations of the method 500, the substrate isheated to facilitate the formation of the light emitting device. In anexample, during the formation of the active layer (operation 515), thesubstrate is heated at a temperature between about 750° C. and 850° C.

FIGS. 6A-6L schematically illustrate a method for forming a lightcoupling layer, in accordance with an embodiment of the invention. FIG.6A shows a light emitting device 600 having an n-GaN layer 605 and abuffer layer 610 over the n-GaN layer 605. The n-GaN layer is formedover an active layer and a p-GaN layer (not shown), which are formedover a substrate, such as a silicon substrate. Next, with reference toFIG. 6B, a metal layer 615 is formed over the buffer layer 610. Themetal layer 615 may be formed on the buffer layer 610 using variousdeposition methods, such as physical vapor deposition (e.g.,sputtering). The metallic material may include one or more of Au, Sn,Ag, Ni and Pt.

Next, with reference to FIG. 6C, a photodefinable layer 620 having aphotodefinable material is deposited on the metal layer 615. Thephotodefinable material in some cases is a photoresist. In an example,the photodefinable material is a photoresist compatible with 157 nm, 193nm, 248 nm or 365 nm wavelength photoresist systems, 193 nm wavelengthimmersion systems, extreme ultraviolet systems (including 13.7 nmsystems) or electron beam lithographic systems. Examples of photoresistmaterials include argon fluoride (ArF) sensitive photoresist, i.e.,photoresist suitable for use with an ArF light source, and kryptonfluoride (KrF) sensitive photoresist, i.e., photoresist suitable for usewith a KrF light source. ArF photoresists may be used withphotolithography systems utilizing relatively short wavelength light,e.g., 193 nm KrF photoresists may be used with longer wavelengthphotolithography systems, such as 248 nm systems. In other cases,nano-imprint lithography (e.g., by using a mold or mechanical force topattern a resist) is used.

Next, with reference to FIG. 6D, a predetermined portion of thephotodefinable layer 620 is removed to define an orifice 625 extendingto the metal layer 615. In some cases, a portion of the photodefinablelayer 620 is exposed to radiation through a reticle and then developedto define the orifice 625 in the photodefinable layer 620. Thepredetermined portion 625 is then removed by washing the exposed anddeveloped portion of the photodefinable layer 620. For example, theorifice is defined in the photodefinable layer by photolithography with248 nm or 193 nm light, in which the photodefinable layer is exposed toradiation through a reticle and then developed. After being developed,the remaining photodefined material forms mask features.

Next, with reference to FIG. 6E, the exposed portion 625 of the metallayer 615 is etched to the buffer layer 610. This may be accomplishedwith the aid of a chemical etchant that selectively etches the metallayer 615 but not the photodefinable layer 620. Suitable chemicaletchants include KCN, KI:I₂, HCl: HNO₃, HNO₃:H₂O, NH₄OH:H₂O₂, sodiumhydroxide and/or potassium hydroxide, an Ar ion-beam sputtering, a Cl₂plasma, an HBr plasma.

Next, with reference to FIG. 6F, the photodefinable layer 620 is removedto expose the layer of the metal layer 615 over the buffer layer 610.The metal layer 615 is then heated to generate metal particles 630 fromthe metal layer, as shown in FIG. 6G. In some cases, the metal layer 615is heated to a temperature less than about 700° C., or less than about600° C., or less than about 500° C., or less than about 400° C., or lessthan about 300° C. Heating may be accomplished with the aid of resistiveheating (e.g., by resistively heating a susceptor supporting thesubstrate, see FIG. 7) and/or exposure of the metal layer 615 toinfrared radiation. The metal particles 630 expose portions of thebuffer layer 610 between the metal particles 630.

Next, with reference to FIG. 6H, the buffer layer 610 is etched to forma roughened buffer layer, which defines the light coupling layer 635.The metal particles 630 are etched away or removed with the aid of achemical etchant that is selective to the metal particles 630. Theportion of the buffer layer 610 not covered by metal particles 630 isetched to the n-GaN layer 605. In some embodiments, the buffer layer isroughened by etching the buffer layer, such as with the aid of anetching process (e.g., wet etching or dry etching). In an example, thebuffer layer is etched with the aid of sodium hydroxide (NaOH),potassium hydroxide (KOH), a Cl₂ plasma, and/or an HBr plasma. In otherembodiments, the buffer layer is roughened by sputtering the bufferlayer. In an example, the buffer layer is roughened by sputtering thebuffer layer with argon (Ar) ions.

In some cases, with the buffer layer 610 formed of u-GaN, AlGaN and AlN,the roughening process removes all of the AlN layer and leaves all orsome of the AlGaN layer over the u-GaN layer. In other cases, theroughening process removes the AlN layer and the AlGaN layer, but leavesat least a portion of the u-GaN layer. In other cases, the rougheningprocess etches a portion of the n-GaN layer 605. Thus, the lightcoupling layer 635 may include n-GaN in addition to the materialincluding the buffer layer 610, such as u-GaN, AlGaN and/or AlN. In somecases, the buffer layer 610 is formed of AlGaN adjacent to the n-GaNlayer 605 and an AlN layer adjacent to the AlGaN layer, and theroughening process etches some or all of the AlN layer and, in somesituations, some of the AlGaN layer.

Next, with reference to FIG. 6I, a photodefinable layer 640 is formedover the light coupling layer 635. The photodefinable layer 640 includesa photodefinable material, such as a photoresist. Next, a portion of thephotodefinable layer 640 is then exposed and developed (e.g., with theaid of a reticle) to form an orifice 645 extending through thephotodefinable layer 640 to the n-GaN layer 605, as illustrated in FIG.6J.

Next, with reference to FIG. 6K, an electrode 650 is formed in theorifice 645. The electrode is formed by depositing one or more metals inthe orifice 645, such as by physical vapor deposition (e.g.,sputtering). The electrode 650 is formed by depositing one or more oftitanium, aluminum, nickel, platinum, gold, silver, rhodium, copper andchromium in the orifice 645. The electrode 650 is in electricalcommunication with the n-GaN layer 605. In the illustrated embodiment,the electrode 650 is in contact with the n-GaN layer 605. Thephotodefinable material is then removed to provide the light couplinglayer 635 over the n-GaN layer 605, as shown in FIG. 6L

As an alternative, following the formation of the orifice 625 (see FIG.6D), the metal layer 615 and the buffer layer 610 are etched to then-GaN layer 605 (i.e., the buffer layer 610 is also removed). Next, theelectrode 650 is formed by depositing one or more metals in the orifice625. The photodefinable layer 620 is then removed and the metal layer is615 is heated to form metal particles over the buffer layer 610. Thebuffer layer 610 is subsequently etched (or roughened) to form the lightcoupling layer 635. In such a case, the electrode 650 may be formed onthe n-GaN layer without the need for the photodefinable layer 640 andthe associated processing operations.

In some embodiments, during the formation of various device layers, thesubstrate is exposed to a Group III precursor and a Group V precursorsimultaneously. In other situations, during the formation of variousdevice layers, the substrate is exposed to the Group III precursor andthe Group V in an alternating fashion—e.g., the Group III precursorfollowed by the Group V precursor, with an intervening purging orevacuation operation. Generally, if a plurality of precursor arerequired to form a device layer, the precursor may be directed into thereaction chamber simultaneously or in an alternating and sequentialfashion.

Device layers may be formed with the aid of various depositiontechniques. In some embodiments, device layers are formed with the aidof chemical vapor deposition (CVD), atomic layer deposition (ALD),plasma enhanced CVD (PECVD), plasma enhanced ALD (PEALD), metal organicCVD (MOCVD), hot wire CVD (HWCVD), initiated CVD (iCVD), modified CVD(MCVD), vapor axial deposition (VAD), outside vapor deposition (OVD) andphysical vapor deposition (e.g., sputter deposition, evaporativedeposition).

While methods and structures provided herein have been described in thecontext of light emitting devices having Group III-V semiconductormaterials, such as, for example, gallium nitride, such methods andstructures may be applied to other types of semiconductor materials.Methods and structures provided herein may be used with light emittingdevices formed at least in part of gallium nitride (GaN), galliumarsenide (GaAs), aluminum gallium arsenide (AlGaAs), gallium arsenidephosphide (GaAsP), aluminum gallium indium phosphide (AlGaInP), galliumphosphide (GaP), indium gallium nitride (InGaN), aluminum galliumphosphide (AlGaP), zinc selenide (ZnSe), aluminum nitride (AlN),aluminum gallium nitride (AlGaN), and aluminum gallium indium nitride(AlGaInN).

Systems Configured to Form Light Emitting Devices

In another aspect of the invention, a system for forming a lightemitting device includes a reaction chamber for holding a substrate, apumping system in fluid communication with the reaction chamber, thepumping system configured to purge or evacuate the reaction chamber, anda computer system having a processor for executing machine readable codeimplementing a method for forming the light emitting device. The codemay implement any of the methods provided herein. In an embodiment, thecode implements a method including providing, in a reaction chamber, asubstrate having disposed thereon a light coupling layer (or structure),the light coupling layer including one or more Group III-V semiconductormaterials, and forming an electrode on a portion of the light couplinglayer, the electrode in electrical communication with one of an n-typesemiconductor layer and a p-type semiconductor layer adjacent to thelight coupling layer. In another embodiment, the code implements amethod including providing, in a reaction chamber, a substrate having abuffer layer, and roughening the buffer layer to form a light couplinglayer.

FIG. 7 shows a system 700 for forming a light emitting device, inaccordance with an embodiment of the invention. The system 700 includesa reaction chamber 705 having a susceptor (or substrate holder) 710configured to hold a substrate that is used to form the light emittingdevice. The system includes a first precursor storage vessel (or tank)715, a second precursor storage vessel 720, and a carrier gas storagetank 725. The first precursor storage vessel 715 may be for holding aGroup III precursor (e.g., TMG) and the second precursor storage vessel720 may be for holding a Group V precursor (e.g., NH₃). The carrier gasstorage tank 725 is for holding a carrier gas (e.g., H₂). The system 700may include other storage tanks or vessels, such as for holdingadditional precursors and carrier gases. The system 700 includes valvesbetween the storage vessels and the reaction chamber 705 for fluidicallyisolating the reaction chamber 705 from each of the storage vessels.

The system 700 further includes a vacuum system 730 for providing avacuum to the reaction chamber 705. The vacuum system 730 is in fluidcommunication with the reaction chamber 705. In some cases, the vacuumsystem 730 is configured to be isolated from the reaction pace 705 withthe aid of a valve, such as a gate valve.

A controller (or control system) 735 of the system 700 facilitates amethod for forming a light emitting device in the reaction chamber 705,such as forming one or more layers of the light emitting device. Thecontroller 735 is communicatively coupled to a valve of each of thefirst precursor storage vessel 715, the second precursor storage vessel720, the carrier gas storage tank 725 and the vacuum system 730. Thecontroller 735 is operatively coupled to the susceptor 710 forregulating the temperature of the susceptor and a substrate on thesusceptor, and the vacuum system 730 for regulating the pressure in thereaction chamber 705.

In some situations, the vacuum system 730 includes one or more vacuumpumps, such as one or more of a turbomolecular (“turbo”) pump, and adiffusion pump and a mechanical pump. A pump may include one or morebacking pumps. For example, a turbo pump may be backed by a mechanicalpump.

In some embodiments, the controller 735 is configured to regulate one ormore processing parameters, such as the substrate temperature, precursorflow rates, growth rate, carrier gas flow rate and reaction chamberpressure. The controller 735, in some cases, is in communication withvalves between the storage vessels and the reaction chamber 705, whichaids in terminating (or regulating) the flow of a precursor to thereaction chamber 705. The controller 735 includes a processor configuredto aid in executing machine-executable code that is configured toimplement the methods provided herein. The machine-executable code isstored on a physical storage medium, such as flash memory, a hard disk,or other physical storage medium configured to store computer-executablecode.

In some embodiments, the controller 735 is configured to regulate one ormore processing parameters. In some situations, the controller 735regulates the growth temperature, carrier gas flow rate, precursor flowrate, growth rate and/or growth pressure.

Unless the context clearly requires otherwise, throughout thedescription and the claims, words using the singular or plural numberalso include the plural or singular number respectively. Additionally,the words ‘herein,’ ‘hereunder,’ ‘above,’ ‘below,’ and words of similarimport refer to this application as a whole and not to any particularportions of this application. When the word ‘or’ is used in reference toa list of two or more items, that word covers all of the followinginterpretations of the word: any of the items in the list, all of theitems in the list and any combination of the items in the list.

It should be understood from the foregoing that, while particularimplementations have been illustrated and described, variousmodifications may be made thereto and are contemplated herein. It isalso not intended that the invention be limited by the specific examplesprovided within the specification. While the invention has beendescribed with reference to the aforementioned specification, thedescriptions and illustrations of embodiments of the invention hereinare not meant to be construed in a limiting sense. Furthermore, it shallbe understood that all aspects of the invention are not limited to thespecific depictions, configurations or relative proportions set forthherein which depend upon a variety of conditions and variables. Variousmodifications in form and detail of the embodiments of the inventionwill be apparent to a person skilled in the art. It is thereforecontemplated that the invention shall also cover any such modifications,variations and equivalents.

What is claimed is:
 1. A light emitting device, comprising: a substrate;a p-type Group III-V semiconductor layer adjacent to the substrate; anactive layer adjacent to the p-type semiconductor layer; an n-type GroupIII-V semiconductor layer adjacent to the active layer; a light couplingstructure adjacent to the n-type Group III-V semiconductor layer, thelight coupling structure comprising one or more Group III-Vsemiconductor materials, wherein the light coupling structure comprisesan orifice extending to the n-type Group III-V semiconductor layer; andan electrode formed in the orifice, the electrode in electricalcommunication with the n-type Group III-V semiconductor layer.
 2. Thelight emitting device of claim 1, wherein the orifice exposes a portionof the n-type Group III-V semiconductor layer.
 3. The light emittingdevice of claim 2, wherein the exposed portion of the n-typesemiconductor layer has a corrugation less than or equal to about 300nanometers (nm).
 4. The light emitting device of claim 1, wherein theorifice has a circular, elliptical, triangular, square, rectangular,pentagonal, hexagonal, heptagonal or nonagonal cross-section.
 5. Thelight emitting device of claim 1, wherein the orifice is a channelextending along at least a portion of the light coupling structure. 6.The light emitting device of claim 1, wherein the one or more GroupIII-V semiconductor materials of the light coupling structure areselected from the group consisting of n-type gallium nitride, u-typegallium nitride, aluminum gallium nitride and aluminum nitride.
 7. Thelight emitting device of claim 1, wherein the n-type Group III-Vsemiconductor layer comprises n-type gallium nitride.
 8. The lightemitting device of claim 1, wherein the p-type Group III-V semiconductorlayer comprises p-type gallium nitride.
 9. The light emitting device ofclaim 1, wherein the electrode comprises one or more elemental metalsselected from the group consisting of titanium, aluminum, nickel,platinum, gold, silver, rhodium, copper and chromium.
 10. The lightemitting device of claim 1, wherein the light coupling structurecomprises one or more light coupling moieties, an individual lightcoupling moiety having a decreasing width along an axis oriented awayfrom the active layer.
 11. The light emitting device of claim 1, whereinthe substrate is selected from the group consisting of silicon,germanium, silicon oxide, silicon dioxide, titanium oxide, titaniumdioxide, sapphire, silicon carbide, a ceramic material and a metallicmaterial.
 12. The light emitting device of claim 1, wherein the lightcoupling structure has protrusions sized between about 10 nanometers(nm) and 3 micrometers (μm).
 13. The light emitting device of claim 1,further comprising an optical reflector between the substrate and thep-type Group III-V semiconductor layer.
 14. The light emitting device ofclaim 13, wherein the optical reflector is formed of one or more ofsilver, platinum, gold, rhodium, aluminum and nickel.
 15. A lightemitting device, comprising: a first layer of a first type of GroupIII-V semiconductor material; a second layer adjacent to the firstlayer, the second layer having an active material configured to generatelight upon the recombination of electrons and holes; a third layeradjacent to the second layer, the third layer comprising a second typeof Group III-V semiconductor material; a light coupling structureadjacent to the third layer, the light coupling structure comprising athird type of Group III-V semiconductor material, the light couplingstructure comprising an opening extending through at least a portion ofthe light coupling structure; and an electrode adjacent to said lightcoupling structure, the electrode in electrical communication with saidone of the first layer and the second layer.
 16. The light emittingdevice of claim 15, wherein the third type of Group III-V semiconductormaterial is different from the first type of Group III-V semiconductormaterial and the second type of Group III-V semiconductor material. 17.The light emitting device of claim 15, wherein the first type of GroupIII-V semiconductor material includes one of an n-type Group III-Vsemiconductor and a p-type Group III-V semiconductor.
 18. The lightemitting device of claim 17, wherein the second type of Group III-Vsemiconductor material includes the other of the n-type Group III-Vsemiconductor and the p-type Group III-V semiconductor.
 19. A method forforming a light emitting device, comprising: providing, in a reactionchamber, a substrate comprising a buffer layer; and roughening a portionof the buffer layer to form a light coupling layer, wherein the lightcoupling layer is formed adjacent to one of an n-type semiconductorlayer and a p-type semiconductor layer, wherein said one of either then-type semiconductor layer or the p-type semiconductor layer is formedadjacent to an active layer, wherein said active layer is formedadjacent to the other of the n-type semiconductor layer and the p-typesemiconductor layer, and wherein said the other of the n-typesemiconductor layer and the p-type semiconductor layer is formedadjacent to the substrate.
 20. The method of claim 19, wherein thebuffer layer comprises one or more Group III-V semiconductor materials.21. The method of claim 20, wherein the buffer layer comprises one ormore of u-type gallium nitride, aluminum gallium nitride and aluminumnitride.
 22. The method of claim 19, further comprising forming anelectrode in electrical communication with said one of the n-typesemiconductor layer and the p-type semiconductor layer.
 23. The methodof claim 19, further comprising forming an opening in the buffer layerextending through at least a portion of the buffer layer.
 24. The methodof claim 23, further comprising forming an electrode in said opening.25. The method of claim 19, wherein roughening the portion of the bufferlayer comprises: forming a layer of a metallic material over the bufferlayer; defining an opening in the layer of the metallic material, theopening extending to the buffer layer; forming metallic particles fromthe layer of the metallic material; and etching the buffer layer.